This invention relates to an improved system and process for preparing comestibles for frozen storage and more particularly to a technique and means for implementation thereof by which a continuing commercial freezing operation may be carried out efficiently and without necessity for mechanically moving conveyance devices as in most, if not all prior flow-through systems. The invention is herein illustratively described by reference to the presently preferred embodiments thereof; however, it will be recognized that certain modifications and changes with respect to details may be made without departing from the essential features involved.
A variety of commercial freezing systems of the flow-through or conveyance line type has evolved over the years in which comestibles, packaged or unpackaged, have been successfully processed as an important area of technology in the food processing industry. In recent years the large part of this activity has been of the type referred to as individualized quick freezing (IQF) wherein the moist comestibles such as shelled peas, cut beans, carrot slices, berries, etc., are frozen before packaging. In those processes the comestibles are deposited on a moving foraminous conveyor means or a foraminous stationary deck in moist condition and are quickly frozen in a so-called "fluidized" state by pressurized freezing air blown upwardly against the individual comestibles causing them to vibrate and tumble in a loose or fluid-like condition as they advance along the conveyor or flow by gravity or otherwise along the supporting surface. The process is efficient and has the important advantage of sealing the individual articles by a quickly formed surface glaze, but in a manner avoiding clumping or agglomeration through ice bonding. Upon completion of the freezing, the discharging individually frozen articles are packaged and then stored for ultimate use. Examples of this technique appear in such prior art U.S. Pat. Nos. 3,477,242, Lamb, et al; 3,169,381, Persson; 2,223,972, Sterling; 3,115,756, Overbye; 3,166,383, Morris; 3,112,186, Davis et al; 3,267,585, Futer; 3,864,931 Guttinger; 3,394,463, Futer; 3,304,619, Futer; and 3,886,762, Rothstein, et al. In some of these and other prior art systems as indicated above, conveyance of the comestibles along the intended path through the freezing chamber is effected by the substantially frictionless gravity induced flow of the comestibles from the input end to the discharge end of the system, much as liquid flows from an initial elevation to a lower elevation. Therefore, it is not novel at this juncture to utilize pressurized freezing air to effect simultaneous conveyance and efficient freezing of comestibles in I.Q.F. (individual quick freezing) without the requirement for mechanically moving conveyor devices and their attendant cost and maintenance problems in such working environments.
However, for many applications it is desirable for a variety of reasons to package the comestibles before freezing. The common implementation of freezing processes for pre-packaged comestibles noted in background references to the present invention, in flow-through or conveyance line systems, employed mechanically moving conveyors for the packages and various arrangements for blowing pressurized freezing air over the surfaces of the packages to effect freezing. The principal problem with such systems has always been a two-fold one, namely, efficient freezing of the containerized comestibles in a short period and, secondly, the problem of cost and space requirements, together with maintenance problems of large mechanized installati ons. In this regard, it will be noted that the usual cardboard or plastic packages employed in the industry form an insulating barrier surrounding the comestibles retarding the rate at which heat can be withdrawn and that this retardation is further aggravated by the existence of air space within the container, usually at the top. Such air space is virtually unavoidable and is indeed desirable as an expansion space to prevent bulging and misshaping of the packages as the comestibles expand on freezing. With past practices, the freezing tunnel installations for pre-packaged comestibles became very long in order to afford an adequate holding period in which to effect complete freezing of the comestibles, thereby making the installation expensive. When adding to this the cost of installation and the associated maintenance problems of a mechanical conveyor system, such as a sprocket driven chain belt or the like, the total installation represented a major undertaking for any commercial processor desiring large volume production rates.
A central object of the present invention is to overcome these difficulties and limitations pertaining to the preparation of pre-packaged comestibles for frozen storage. More specifically, a broad object hereof is to devise a flow-through system and a process wherein containerized or pre-packaged comestibles may be frozen efficiently and quickly in an installation that utilizes a conveyor run of minimum length and more particularly, in an installation of such a conveyor run that occupies minimum floor space and dispenses altogether with the need for mechanically moving conveyor mechanisms.
A related or subsidiary object hereof is to devise such a system and process wherein the pressurized freezing air available from conventional or, if desired, specially designed devices, is utilized to maximum advantage and for multiple purposes in both the effective freezing of the packaged comestibles in a minimum time period and in effecting the conveyance of the comestibles during freezing. More specifically, the technique employs a means utilizing the packages themselves and an apertured conveyance deck cooperatively for partially entrapping and confining the flow of pressurized air against and along the package surfaces so as to withdraw heat from the comestibles through the package bottom and side walls at maximum rate while simultaneously suspending the packages on an air layer or film that also permits substantially frictionless conveyance and indeed, may partially propel the packages in the desired direction of conveyance. With the package lying flat supported on the high velocity film of air, maximum heat transfer rate is thus achieved by the freezing air inasmuch as it is primarily through the package bottoms and adjoining side walls of the packages that the potential for heat transfer is by far the greater. In addition, the invention employs an efficient means of the described nature that effectively utilizes gravity flow of the packages, together with a plenum and collecting system of ducting for the air in association with the multiply apertured conveyance deck that can be constructed at minimum cost and with minimum floor space requirements in a processing plant.
A further object hereof is to provide such a system that can be implemented in a highly simple and relatively small installation for economy applications by small processors, or as well can be implemented in a more elaborate and highly productive installation to even greater advantage, proportionately, for larger installations where volume of production or freezing requirements applied to larger packages so indicate.
Ease of accessibility for inspection, cleaning and troubleshooting, such as where packages accidentally become stuck or may tend to pile up within the system represents a further objective of the invention in its preferred embodiment. Likewise, controllability of freezing rate and/or pressurized freezing air flow rate in the system represents still another objective.
These and various other purposes of the invention will become more fully evident as the description proceeds.